To be able to measure with scalability among possibly millions of endpoints, a communications network can be segmented such that every segment measurement is highly leveraged. High delay percentile metrics are known to be good indicators of network performance. Unfortunately, there is no simple way known to estimate end-to-end high delay percentiles given concatenated network percentiles for arbitrary delay distributions.
The definition of network performance objectives is becoming increasingly important as Internet Protocol (IP)-based services are more widely deployed in service provider networks. The ITU-T Recommendation Y.1541, entitled “Network Performance Objectives for IP-based Services,” defines classes of network Quality of Service (QoS), and specifies objectives for IP network performance parameters. The Recommendation Y.1541 is currently under revision to consider providing rules for using measurements of segments of a path and combining the measured values to estimate the User-Network Interface (UNI) to UNI IP performance.
One of the more difficult performance parameters to estimate on an end-to-end basis is the IP Packet Delay Variation (IPDV), also referred to as jitter. The IPDV for a particular percentile delay is defined as follows:DV99.9=99.9th percentile delay−referenceDV99.8=99.8th percentile delay−reference
etc.
where “reference” can be the mean or minimum delay. It has been difficult to estimate the end to end percentile delay from segment delay percentiles.
In Y.1541, a proposed tabular method suggests the number of segments of a given delay variation that are allowed such that a 50 ms IPDV objective can be met. Put another way, this tabular method provides suggested requirements on how to meet a single end-to-end IPDV value by limiting the IPDV for various numbers of segments. This tabular approach is not very flexible. For example, since the current table is based on a 50 ms IPDV objective, to determine whether a 40 ms IPDV objective has been met would require creating a new table. Another approach proposes an approximation method for combining the quantiles and the third central moments of the delay variation of path segments into the desired end-to-end values. This latter approach is mathematically complex and considered unworkable.